Conventionally, a variety of noncentrifugal blood collection tubes have been proposed wherein a blood sample is collected by a vacuum blood collection needle by utilizing reduced pressure in a container and the blood is filtered through a filter member accommodated in the container. Such blood collection tubes are disclosed, for example, in Japanese Unexamined Patent Publication No. 2002-277357, Japanese published Patent No. 3015854, Japanese Unexamined Patent Publication No. 11-290297 (1999), Japanese Unexamined Patent Publication No. 4-20856 (1992) and Japanese Unexamined Patent Publication No. 2001-321365.
In a conventional noncentrifugal sample collecting container, a plug member is pierced with a vacuum blood collection needle and blood is collected using reduced pressure. Then the collected blood is filtrated through a filter member located in the sample collecting container or combined with the sample collecting container. In this case, the vacuum blood collection needle is removed after completion of the blood collection. The collected blood passes through the filter member owing to the reduced pressure remaining in the lower part of the filter member, namely in the part into which filtrated blood is to be stored. In brief, blood is filtrated by a pressure difference between upside and downside of the filter member.
However, when the pressures of upside and downside of the filter member reach equilibrium, the driving force for filtration is cancelled so that the filtration stops. For this reason, in order to promote the filtration, it was conventionally necessary to make the upside of the filter member to be atmospheric pressure by detaching the plug member above the filter member to generate a pressure difference between downside and upside of the filter member. In this procedure, however, since the plug member of sample collecting container storing a collected blood sample need to be detached, the operator is susceptible to infection by adhesion of blood. In addition, when the plug member is removed from the sample collecting container, the space over the filter member is widely exposed to the exterior to lead a risk of contamination by foreign matters.
A sample collecting container disclosed in Japanese Unexamined Patent Publication No. 11-290297 (1999) has such a structure that an inner tube provided with a filter member in a lower part is hermetically inserted into an outer tube, and filtration is promoted by lowering the pressure in a space under the filter member in the outer tube by moving the inner tube in the direction of removing it from the outer tube. In this structure, however, the driving force required for filtration is inadequate only by the pressure difference obtainable by the above operation, so that filtration may possibly stop during the filtration process.
In a sample collecting container disclosed in Japanese Unexamined Patent Publication No. 4-20856 (1992), a collection container for collecting a filtered sample, which is sealed with a plug and depressurized in advance, and a sample collecting container in which blood has been collected are connected via a filter member, and the blood sample in the sample collecting container is allowed to pass through the filter member by the reduced pressure in the collection container for collecting a filtered sample. In this approach, the degree of depressurization in the sample collecting container is relatively higher, however, there is still fear that filtration stops during the filtration process.